Although testosterone replacement therapy (TRT) is the first-choice method used worldwide for late-onset hypogonadism (LOH), clinical benefits are not seen in all cases. This study was conducted to determine the predictors of TRT efficacy for LOH. Fifty-six patients who visited our Men's Health Clinic (Kawanishi City Medical Center, Kawanishi and Hyogo Medical University, Nishinomiya, Hyogo, Japan) between November 2003 and June 2021 with data available before and after TRT were enrolled. They were divided into responders (Group 1; n = 45, accounting for 80.4%) and nonresponders (Group 2; n = 11, accounting for 19.6%) based on the clinical response to TRT, including patient satisfaction. Factors noted before TRT included age, body mass index, aging males' symptoms score, sexual health inventory for men, luteinizing hormone, follicular-stimulating hormone, testosterone, free testosterone, prolactin (PRL), estradiol (E2), and testosterone/estradiol (T/E2) ratio in serum. For statistical analysis, a multivariable logistic regression model was used. Univariate analysis revealed PRL (odds ratio [OR]: 0.9624; 95% confidence interval [CI]: 0.9316-0.9943, P < 0.05), E2 (OR: 0.8692; 95% CI: 0.7745-0.9754, P < 0.05), and T/E2 ratio (OR: 1.1312; 95% CI: 1.0106-1.2661, P < 0.05) to be predictive factors. Multivariate analyses showed that T/E2 ratio was an independent predictive factor (OR: 1.1593; 95% CI: 1.0438-1.2875, P < 0.01). The present results suggest that a low value for T/E2 ratio may predict a reduced response to TRT. The T/E2 ratio threshold to predict nonresponders based on receiver-operating characteristics (ROC) curve analysis was shown to be 17.3. Although additional studies with larger number of patients are necessary, we propose the determination of serum E2 level and testosterone level prior to performing TRT.

Keywords: estradiol; late-onset hypogonadism; predictive factor; testosterone; treatment.

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